Leachate and pollution control barriers and systems have been developed in recent times for purposes of containing, confining, and removing pollutants from waste storage, land fills, chemical storage areas, dumps, and nuclear waste storage facilities as disclosed in Ressi applicationn Ser. No. 252,676 and my patent application Ser. No. 468,724. In Veder U.S. Pat. No. 3,310,952, a bentonite slurry trench is made in the earth wherein the trench is backfilled with a gravel so as to erect a porous wall for the purpose of draining. There, the excavation was filled with gravel and sand of a size of grain adapted to the condition of the ground and to take care of simultaneous washing of the walls of the excavation so as to remove the sealing effect caused by the impermeable zone of bentonite. In that invention, the mixture of gravel and sand is brought into the trench in a permeable enclosure so as to prevent the penetration of the gravel into the surrounding soil. F. And G. Brunner's British Pat. No. 913,527 disclose the use of a slurry trench to lay pipe and the above referred to Ressi application discloses a cut-off barrier in which a porous fill with a pump system is sandwiched between a pair of plastic films which are joined along their bottom edges to form a sheath. For many years, there has been commercially available from American Colloid Corporation and others, a drilling mud useful in making water wells which drilling mud has a highly viscous character which, after a predetermined period of time, for example about 5 days, changes to almost the viscosity of water.
In the present invention, a drainage ditch is formed by excavating a narrow slot in the earth in the presence of a mud slurry having a highly viscous character which reverts or changes to a low viscosity after a period of time needed to maintain the trench open to permit the laying of a drainage pipe at the bottom of the trench and filling with a pervious fill such as gravel and sand mixed. After the gravel and sand mix has been installed, lateral support for the earth walls is provided by the pervious material and the slurry then reverts to a low viscosity liquid which may be drained via the drain pipe in the bottom of the drainage trench. In addition, a plastic film or layer may be installed in the trench opposite the the land fill or pollutant side a source to constitute an impervious membrane installed prior to filling with the porous fill material. Preferably, the film is installed on one side of the trench.
There are many advantages resulting from use of the invention such as it allows for the installation of a system to great depth, excavating a narrow slot which may be only two feet wide. The invention also allows for the installation of an impervious barrier as well as a leachate and pollution collection system. Since the excavation is narrow (two feet wide is typical), it minimizes the exposure to workers and the public when installation is to be made in a hazardous environment. In addition, since the trench is always maintained filled during excavation with the revertable slurry, noxious gases which may tend to escape when the trench is opened are contained and do not escape. The invention also reduces the amount of contaminated earth to be disposed of becaue of the narrowness of the slot or trench in the earth. Finally, the invention eliminates the handling of contaminated water to be pumped as in a conventional approach.